Gel formation in polymers can be caused during the isolation and drying of the polymers from either an aqueous system or a solvent or cement system wherein localized polymer hot-spots can result in the undesirable gelling or cross-linking phenomenon. Care must be taken to assure that during the processing of elastomers that the polymer's structure is not altered which will result in degradation of the polymer's physical properties.
The process for solution polymerization of synthetic elastomers such as polybutadiene is well known in the art. Monomer and solvent are purified and dried. The catalyst is prepared separately and then added to the reaction vessel containing the monomer or monomers, for example, butadiene and styrene. When the desired degree of polymerization has been achieved, the catalyst is deactivated, the unreacted monomer or monomers and solvent are removed, and the polymer is recovered, washed, dried and baled. It is usually during the recovery process, where the elastomer is dewatered and dried that the formation of gel occurs.
Japanese Patent No. 49,066,725 discloses gelation inhibitors that are obtained by mixing solid phenylenediamine derivatives with liquid reaction products derived from aromatic amines and acetone. This patent discloses a stable suspension consisting of 100 parts of a 1:3 mixture of 4-(isopropyl-amino) diphenylamine and a toluidine-acetone condensate, 293 parts water, 2.5 parts of a 50% aqueous solution of KOH, and 4.5 parts of oleic acid. This suspension was then combined with an SBR latex at ratios of the suspension to the SBR of about 0.6:100. The rubber mixture was then flocculated to give rubber with 20% gel after 130 hours at 120.degree. C. compared to 80% gel for rubber containing dodecylphenylamine in place of the subject suspension.
U.S. Pat. No. 3,984,372 and 4,168,387 which are incorporated herein by reference disclose esters of polyphenolics as polymerizable or built-in antioxidants. These patents disclose the use of compounds such as 2-(2-hydroxy-3-tert.butyl-5-methylbenzyl)-4-methyl-6-tert.butyl phenyl methacrylate as polymerizable antioxidants for polymeric compositions. More specifically, the compounds of these two U.S. Patents are reaction products of a polyphenolic compound such as 2,6-bis-(2-hydroxy-3-tert.butyl-5-methylbenzyl)-4-methylphenol; and 2,2'-methylene-bis-(4-methyl-6-tert.butylphenol) with an ester forming compound of the general formula: ##STR1## wherein R.sup.3 is selected from the group consisting of hydrogen and alkyl radicals having from 1 to 4 carbon atoms, R.sup.4 is selected from the group consisting of hydrogen and alkyl radicals having from 1 to 4 carbon atoms, and wherein A is selected from the group consisting of chlorine, iodine and bromine.
U.S. Pat. No. 4,707,300, which is incorporated herein by reference relates to the reaction products of an acid catalyzed simultaneous reaction between a phenol, formaldehyde and a mercaptan in specific molar ratios under specific reaction conditions. The reaction product is normally a liquid at room temperature and exhibits excellent antidegradative properties in oxidizable materials. Further, this U.S. patent is concerned with the autosynergistic phenolic reaction product itself and its incorporation into oxidizable organic materials.
The invention of this disclosure is directed to the discovery that the combination of materials disclosed in U.S. Pat. Nos. 3,984,372 and 4,168,387 with those of U.S. Pat. No. 4,707,300 lessen or prevents the formation of gel in elastomers.
There is a need in the rubber industry for a process or system which will prevent or greatly lessen the formation of gel during the isolation and processing of natural or synthetic elastomers.